Peter Davis

Demonstration of robust multi-hop wireless packet broadcasts for moving vehicles using aggregated redundancy

We demonstrate a method for improving quality of ad-hoc multihop wireless communications between moving vehicles. This method is designed to overcome problems of high packet loss and route instability common in inter-vehicular communications. We implemented the proposed method as middleware supporting real-time packet transmissions such as VoIP, and evaluated the performance in experimental tests, including a 3-vehicle test on a public road. We obtained measurement results showing maximum packet loss lower than 5 %, compared to more than 80% with existing implementations of the ad hoc routing protocols OLSR and AODV. We also showed that it is possible to support good quality VoIP broadcasts at normal traffic speeds of from 40km/h to 60 km/h on open roads.

Evaluation of Linux Bonding Features

The paper contains an evaluation of the current Linux bonding implementation for wired interfaces. The Linux bonding provides methods to aggregate multiple wired interfaces to support load balancing, fault-tolerance and throughput improvement. The intention is to identify the performance of the current Linux bonding implementation and to use the results and assumptions for future discussions about bonding of wireless interfaces. The paper presents details about interface bonding in a RedHat Linux system and discusses measurement results of two bonded LAN interfaces using the round-robin bonding mode.

Achieving stable operation of ad hoc wireless networks with neighbor pre-selection and synchronous route updates

We propose two methods for improving the stability of communication in ad hoc wireless networks - firstly, the selection of reliable neighbors for data relay based on monitoring signal strength variations and secondly, the synchronous update of routing tables. These methods were designed to overcome problems observed in recent large testbed experiments. We show the dramatic improvement in stability and reduction of packet error rate which was achieved when we introduced these methods to an implementation of the OLSR routing protocol. Specifically we evaluated performance in a 50-node ad hoc wireless network, and showed a reduction in the packet error rate from 12% to less than 1

Aggregation of Wi-Fi Links: When Does it Work?

We conducted a systematic experimental and simulation study on the behaviour of aggregated Wi-Fi links for WLAN access. The Wi-Fi links were aggregated by bonding multiple Wi-Fi interfaces. We demonstrated a close to linear improvement in maximum throughput with the number of aggregated links. We analyse unstable behaviour which appears in both UDP and TCP based applications when flows are split over multiple Wi-Fi links, even when the links are statistically symmetric. We show that this unstable behaviour is due to the short term variations in packet latencies, and occurs in distinct regimes, starting before the saturation of throughput. Our analysis suggests that since the origin of the instability is local, it could be suppressed by intelligent control applied locally at the wireless interfaces.

Interface Status Monitoring for Wireless Link Aggregation in Cognitive Networks

In wireless communication networks, there is growing interest in using mobile terminals with multiple wireless interfaces in order to achieve increased throughput and reliability. However, the performance of communications using multiple wireless interfaces can be severely impaired by fluctuations in quality of the wireless links. We designed and implemented a novel interface status monitoring scheme which supports the detection of changes in wireless link characteristics for multiple wireless interfaces and proactive decision making about the status of interfaces which can be used for communication. The monitoring scheme acquires information about link quality parameters, such as signal strength, retries and rate, directly from the wireless device driver, which allows it to acquire a large amount of information about wireless transmissions available in the driver, and to reduce latency in deciding the status of interfaces. In this paper we describe the design of the scheme and demonstrate its application to sustaining throughput on aggregated Wi-Fi links.

Breakthroughs in Large-Scale Ad Hoc Wireless Networking and Application for Vehicle Safety

Ad hoc wireless networks are expected to have many useful applications, such as emergency communications after accidents and natural disasters, distributed sensing in buildings and natural environments, versatile wireless monitoring in health care and support system, and to make our daily lives easier, more productive and more enjoyable. In order to fully realize the potential of wireless ad hoc networks, we need to be able to realize large-scale networks, which connect large numbers of ad hoc terminals over wide areas. Previous research on ad hoc networks has been based mainly on computer simulations and small-scale implementations, and there have been few successful implementations of large-scale ad hoc networks. We have made significant breakthroughs toward realizing real-world operation of large-scale ad hoc networks, by the testbed based approach. In this paper, we discuss the breakthroughs toward realizing large-scale ad hoc networks and inter-vehicle communications for vehicle safety, which is one of the promising applications of ad hoc networks.

Packet aggregation at access points for concurrent real-time interactions over wireless relay networks

We propose and demonstrate a method for improving capacity for real-time interactive communications over multi-hop wireless networks using WiFi wireless devices. The proposed method uses aggregation of packets at access points designed to avoid bottlenecks in relay traffic and maintain low end-to-end latency. We present experimental results which demonstrate that a relay node can support seven concurrent voice-over-IP (VoIP) sessions using a single 802.11 channel.

Evaluation of packet latency and fluctuation during UDP packet exchange in ad hoc wireless groups

We study latency fluctuation during UDP packet exchange in ad hoc wireless groups. We focus on wireless media access using carrier sensing multiple access with collision avoidance, specifically the 802.11 protocol. We show that there can be large intermittent fluctuations in transmission times when packet exchange is done using UDP unicast. We show how the conditions for the onset of large fluctuations can be estimated, and how these estimates can be used in the design of applications which require real-time data exchanges with low latency.

Content Propagation Analysis of E-mail Communications

We analyze email communications within a large company to reveal how email activity patterns depend on content. We characterize email contents using keywords and examine statistics of email transmissions. As a result, we are able to identify differences in network structures and propagation behaviors depending on the type of keyword.We analyze email communications within a large company to reveal how email activity patterns depend on content. We characterize email contents using keywords and examine statistics of email transmissions. As a result, we are able to identify differences in network structures and propagation behaviors depending on the type of keyword.

First-use analysis of communication in a social network

The study of communication activity in social networks is aimed at understanding and promoting communications in groups, organizations and communities. In this paper, we propose a method for the analysis of communication records to extract content-based network activity, with a focus on first-use. Links between people in a social network are defined based on content and temporal relation of messages sent and received. We introduce the notion of first-use, first-use paths, and classes of users based on first-usage. First-use is defined with respect to a specific time period and specific communication content. It refers to the sending of messages containing the specified contents for the first time before being receiving them from any other user in the specified time period. First-use paths are defined as sequences of first-use events in communication networks, and m-ary classes of users are defined recursively as users who receive for the first time from (m-1)-ary users. We present an example of application of the analysis to the email records of a large company.